Method for refining magnetic domains of grain-oriented electrical steel plates, and apparatus therefor

ABSTRACT

Provided is a method for refining magnetic domains of grain-oriented electrical steel plates including: a steel plate supporting roll position adjusting step of controlling a vertical direction position of the steel plate while supporting the steel plate; a laser radiating step of melting the steel plate by radiating a laser beam to form grooves on the surface of the steel plate; and a setting and maintaining step of setting and maintaining an internal operation environment of a laser room in which the laser radiation is performed, so as to increase magnetic domain refinement efficiency and improve workability by optimizing equipment and processes, thereby increasing the processing capacity.

TECHNICAL FIELD

The present invention relates to a method for refining magnetic domainsof grain-oriented electrical steel plates and an apparatus thereof,which permanently refine magnetic domains of steel plates by radiating alaser to the grain-oriented electrical steel plates.

BACKGROUND ART

For example, a grain-oriented electrical steel plate with magneticcharacteristics such as low iron loss and high magnetic flux density isrequired in order to reduce power loss and improve efficiency ofelectric devices such as a transformer.

There is disclosed a technique of refining magnetic domains in avertical direction to a rolling direction by a mechanical method orradiating a laser beam to a surface of the steel plate so as to reducethe iron loss of the grain-oriented electrical steel plate.

The method for refining the magnetic domains may be broadly divided intotemporal magnetic domain refinement and permanent magnetic domainrefinement depending on whether or not an effect of improving magneticdomain refinement after the stress removing and annealing is maintained.

The temporal magnetic domain refinement method has a disadvantage oflosing the magnetic domain refinement effect after the stress removingand annealing. In the temporal magnetic domain refinement method, themagnetic domains are refined by forming a local compression stressportion on the surface of the steel plate. However, such a method causesdamage to an insulating coating layer on the surface of the steel plateand thus, recoating is required, and there is a disadvantage that themanufacturing cost is high because the magnetic domain refinement isperformed in an intermediate process rather than a final product.

The permanent magnetic domain refinement method may maintain an effectof improving the iron loss even after heat treatment. For the permanentmagnetic domain refinement, techniques using an etching method, a rollmethod, and a laser method have been mainly used. In the case of theetching method, it is difficult to control groove formation depth andwidth, and it is difficult to guarantee the iron loss property of thefinal product, and it is disadvantageous in that the etching method isnot eco-friendly because an acid solution is used. In the case of themethod using the roll, there is a disadvantage that the stability,reliability, and process are complicated for mechanical processing.

In the method for refining the magnetic domains of the steel plate byusing a laser, molten grooves are formed on the surface of the steelplate by radiating a laser beam to the surface of the steel plate whilethe steel plate is supported and the tension is adjusted, therebyrefining magnetic domains. As described above, in order to refine themagnetic domains using the laser, it is required to improve and optimizethe process more effectively so that the iron loss of the electric steelplate is reduced and the magnetic flux density is increased whilehigh-speed processing can be performed.

DISCLOSURE Technical Problem

The present invention has been made in an effort to provide a method forrefining magnetic domains of a grain-oriented electrical steel plate andan apparatus thereof having advantages of enhancing efficiency ofmagnetic domain refinement and improving workability by optimizingequipments and processes, thereby enhancing processing capacity.

The present invention has been also made in an effort to provide amethod for refining magnetic domains of a grain-oriented electricalsteel plate and an apparatus thereof having advantages of enhancing moreiron loss improvement efficiency and minimizing reduction of magneticflux density.

The present invention has been also made in an effort to provide amethod for refining magnetic domains of a grain-oriented electricalsteel plate and an apparatus thereof having advantages of enhancingquality of products by more efficiently removing contaminants such ashill up and spatters formed by laser radiating.

The present invention has been also made in an effort to provide amethod for refining magnetic domains of a grain-oriented electricalsteel plate and an apparatus thereof having advantages of providing anoptimal operating environment required for processes.

Technical Solution

An exemplary embodiment of the present invention provides a method forrefining magnetic domains of a grain-oriented electrical steel plateincluding: a steel plate supporting roll position adjusting step ofcontrolling a vertical direction position of the steel plate whilesupporting the steel plate; a laser radiating step of melting the steelplate by radiating a laser beam to form grooves on the surface of thesteel plate; and a setting and maintaining step of setting andmaintaining an internal operation environment of a laser room in whichthe laser radiation is performed.

The method for refining the magnetic domains may further include a warpcontrol step of allowing the steel plate to move along the center of aproduction line without horizontal biasing.

The method for refining the magnetic domains may further include atension control step of applying tension to the steel plate so as tokeep the steel plate in a flatly unfolded state.

The setting and maintaining step may include steps of isolating theinside of the laser room from the outside to block the inflow ofexternal contaminants, and controlling an internal temperature,pressure, and humidity of the laser room.

The method for refining the magnetic domains may further include apost-treatment step of removing hill up and spatters formed on thesurface of the steel plate through the laser radiating step.

The post-treatment step may include a brushing step of removing the hillup and the spatters smeared on the surface of the steel plate by a brushroll.

The post-treatment step may further include a cleaning step ofadditionally removing the hill up and the spatters remaining on thesurface of the steel plate by electrolytically reacting the steel platewith an alkali solution and a filtering step of filtering foreignsubstances included in the alkali solution removed from the steel platein the cleaning step from the alkali solution.

The warp control step may include a warp amount measuring step ofmeasuring a warp amount when a width center position of the steel platedeviates from the center of the production line, and a warp amountcontrolling step of controlling a warp amount of the steel plate byrotating and moving a shaft of the steering roll according to the warpamount of the steel plate measured in the warp amount measuring step toadjust the moving direction of the steel plate.

In the warp amount controlling step, the warp amount of the steel platemay be controlled within ±1 mm.

The tension controlling step may include a steel plate tension applyingstep of applying tension to the steel plate by the tension bridle roll,a steel plate tension measuring step for measuring the tension of thesteel plate subjected to the steel plate tension applying step, and asteel plate tension controlling step of controlling the tension of thesteel plate by adjusting a speed of the tension bridle roll according tothe tension of the steel plate measured in the steel plate tensionmeasuring step.

The steel plate supporting roll position adjusting step may include asteel plate supporting step of supporting the steel plate positioned inthe laser radiating step by the steel plate supporting roll, abrightness measuring step of measuring brightness of a flame occurringwhen the laser is radiated to the steel plate in the laser radiatingstep, and a steel plate supporting roll position control step ofcontrolling the steel plate to be located within a depth of focus of thelaser by adjusting the position of the steel plate supporting roll bythe steel plate supporting roll position control system according to thebrightness of the flame measured in the brightness measuring step.

The laser radiating step may include a laser radiating and energytransmission step of forming grooves having an upper width, a lowerwidth and a depth within 70 μm, within 10 μm, and 3 to 30 μm,respectively, by radiating the laser beam radiated from the laseroscillator to the surface of the steel plate by the optical system, andsimultaneously transmitting to the steel plate the laser beam energydensity within the range of 1.0 to 5.0 J/mm² required for the melting ofthe steel plate so that a re-coagulation part remaining on the innerwall surface of the groove of the melting part is generated during thelaser beam radiating.

The laser radiating step may include a laser beam oscillation controlstep of controlling the laser oscillator oscillating the laser beam toturn on under normal operation conditions by a laser oscillatorcontroller and controlling the laser oscillator to turn off when thesteel plate warp amount is 15 mm or more.

In the laser radiating step, the laser oscillator may oscillate aGaussian energy distribution continuous wave laser beam.

In the laser radiating step, the optical system may adjust an intervalof the laser beam radiation line to 2 to 30 mm in the rolling directionby controlling a laser scanning speed.

The laser radiating step may further include an angle changing step ofchanging a radiation line angle of the laser beam radiated on thesurface of the steel plate.

In the angle changing step, the radiation line angle of the laser beamwith respect to the width direction of the steel plate may be changed toa range of ±4°.

In the laser radiating step, with respect to the surface of the steelplate progressing in contact with the surface of the steel platesupporting roll in the form of an arc, by setting as a reference pointan radiating position of the laser beam when the radiating direction ofthe laser beam passes through a central axis of the steel platesupporting roll, the laser beam may be radiated to a position separatedat a angle along an outer peripheral surface from the center of thesteel plate supporting roll at the reference point.

In the laser radiating step, the laser beam may be radiated in a rangeof 3 to 7° separated from the center of the steel plate supporting rollalong the outer peripheral surface thereof with respect to the referencepoint.

The laser radiating step may further include a shielding step ofshielding scattering light and heat of the laser beam from flowing intothe optical system of the laser radiating equipment.

The laser radiating step may further include a dust collecting step ofsucking and removing the fumes and the molten iron generated when thelaser beam is radiated.

The dust collecting step may include a spraying step of removing themolten iron remaining in the grooves by spraying compressed dry air intothe grooves of the steel plate.

Another exemplary embodiment of the present invention provides anapparatus for refining magnetic domains of a grain-oriented electricalsteel plate including: a steel plate supporting roll position adjustingequipment of controlling a vertical direction position of the steelplate while supporting the steel plate; a laser radiating equipment ofmelting the steel plate by radiating a laser beam to form grooves on thesurface of the steel plate; and a laser room of accommodating the steelplate supporting roll position adjusting equipment and the laserradiating equipment separately from the outside and providing anoperating environment for radiating the laser.

The apparatus for refining magnetic domains may further include a warpcontrol equipment for allowing the steel plate to move along the centerof the production line without horizontal biasing.

The apparatus for refining magnetic domains may further include atension control equipment for applying tension to the steel plate so asto keep the steel plate in a flatly unfolded state.

The laser room may accommodate the laser radiating equipment and thesteel plate supporting roll position adjusting equipment to form aninternal space to separate the equipments from the outside and has aninlet and an outlet formed at both sides in a progressing direction ofthe steel plate, and include a positive pressure device for raising theinternal pressure of the laser room therein, an optical system lowerframe separating an upper space in which the optical system of the laserradiating equipment is positioned from a lower space through which thesteel plate passes, and a constant temperature and humidity controllerfor controlling the internal temperature and humidity of the laser room.

The apparatus for refining magnetic domains may further include apost-treatment equipment for removing hill up and spatters formed on thesurface of the steel plate.

The post-treatment equipment may include a brush roll which is disposedat the rear end of the laser room to remove the hill up and the spatterson the surface of the steel plate.

The post-treatment equipment may further include a cleaning unit whichis disposed at the rear end of the brush roll to additionally remove thehill up and the spatters remaining on the surface of the steel plate byelectrolytically reacting the steel plate with an alkali solution and afiltering unit which is connected to the cleaning unit to filter foreignsubstances included in the alkali solution of the cleaning unit from thealkali solution.

The warp control equipment may include steering rolls for shifting amoving direction of the steel plate, a warp measurement sensor formeasuring a degree (warp amount) when a width center position of thesteel plate deviates from the center of the production line, and a steelplate center position control system for controlling a moving directionof the steel plate by rotating and moving shafts of the steering rollsaccording to the output value of the warp measurement sensor.

The tension control equipment may include tension bridle rolls forguiding movement of the steel plate while applying a tension to thesteel plate, a steel plate tension measuring sensor for measuring thetension of the steel plate passing through the tension bridle roll, anda steel plate tension control system for adjusting speeds of the tensionbridle rolls according to the tension of the steel plate measured by thesteel plate tension measuring sensor.

The steel plate supporting roll position adjusting equipment may includea steel plate supporting roll for supporting the steel plate to theposition of the laser radiating equipment, a brightness measurementsensor for measuring brightness of flame occurring when the laser isradiated to the steel plate in the laser radiating equipment, and asteel plate supporting roll position control system for controlling theposition of the steel plate supporting roll in accordance with thebrightness of the flame measured by the brightness measurement sensor.

The laser radiating equipment may include a laser oscillator foroscillating a continuous wave laser beam, and an optical system offorming grooves having an upper width, a lower width and a depth within70 μm, within 10 μm, and 3 to 30 μm, respectively, by radiating thelaser beam oscillated from the laser oscillator onto the steel platesurface, and simultaneously transmitting to the steel plate the laserenergy density within the range of 1.0 to 5.0 J/mm² required for themelting of the steel plate so that a re-coagulation part remaining onthe inner wall surface of the groove of the melting part is generatedduring the laser radiating.

The laser radiating equipment may further include a laser oscillatorcontroller of controlling the laser oscillator to turn on under normaloperation conditions by a laser oscillator controller and controllingthe laser oscillator to turn off when the steel plate warp amount is 15mm or more.

The laser oscillator may oscillate a Gaussian energy distributioncontinuous wave laser beam.

The optical system may adjust an interval of the laser radiation line to2 to 30 mm in the rolling direction by controlling a laser scanningspeed.

The laser radiating equipment may have a structure which is rotatable bythe driver to change the angle of the radiation line of the laser beamwith respect to the width direction of the steel plate by rotating theoptical system with respect to the steel plate.

The laser radiating equipment may radiate the laser beam to a positionseparated at a angle along an outer peripheral surface from the centerof the steel plate supporting roll at a reference point, by setting asthe reference point an radiating position of the laser beam when theradiating direction of the laser beam passes through a central axis ofthe steel plate supporting roll, with respect to the surface of thesteel plate progressing in contact with the surface of the steel platesupporting roll in the form of an arc.

The laser radiating equipment may radiate the laser beam in a range of 3to 7° separated from the center of the steel plate supporting roll alongthe outer peripheral surface thereof with respect to the referencepoint.

The laser radiating equipment may further include a shielding unit ofshielding laser scattering light and heat from flowing into the opticalsystem.

The laser radiating equipment may further include molten iron removingequipment for removing fumes and spatters generated by radiating thelaser beam to the steel plate.

The molten iron removing equipment may include an air knife for sprayingcompressed dry air into the grooves of the steel plate to remove molteniron remaining in the grooves, and dust collecting hoods for sucking andremoving the fumes and the molten iron.

Advantageous Effects

According to the exemplary embodiment of the present invention, it ispossible to secure iron loss improvement rates before and after heattreatment of an electrical steel plate at 5% or more and 10% or more,respectively, by stably performing a magnetic domain refining process bya laser while the steel plate is moved at a high speed of 2 m/sec ormore.

Further, it is possible to enhance the magnetic domain refiningefficiency and improve the workability, thereby increasing the magneticdomain refining ability.

Further, it is possible to further improve the iron loss improvementefficiency and minimize deterioration of the magnetic flux density.

Further, it is possible to enhance the quality of products by moreefficiently removing contaminants such as hill up and spatters formed bylaser radiating.

Further, it is possible to mass-produce high-quality products byproviding an optimal operating environment required for processes.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration of anapparatus for refining magnetic domains of a grain-oriented electricalsteel plate according to the present exemplary embodiment.

FIG. 2 is a schematic diagram illustrating a steel plate subjected tomagnetic domain refinement according to the present exemplaryembodiment.

FIG. 3 is a schematic diagram illustrating a configuration of an opticalsystem of a laser radiating equipment according the present exemplaryembodiment.

MODE FOR INVENTION

The terms used below is for the purpose of describing specific exemplaryembodiments only and are not intended to be limiting of the presentinvention. The singular forms used herein include plural forms as well,if the phrases do not clearly have the opposite meaning. The “including”used in the specification means that a specific feature, region,integer, step, operation, element and/or component is embodied and otherspecific features, regions, integers, steps, operations, elements,components, and/or groups are not excluded.

Hereinafter, exemplary embodiments of the present invention will bedescribed so as to be easily implemented by those skilled in the art,with reference to the accompanying drawings. As those skilled in the artwould realize, the described embodiments may be modified in variousdifferent ways, all without departing from the spirit or scope of thepresent invention. Therefore, the present invention can be implementedin various different forms, and is not limited to the exemplaryembodiments described herein.

In the following description, as the present exemplary embodiment,equipment for permanent magnetic domain refinement of a grain-orientedelectrical steel plate used in a transformer iron core material and thelike will be described.

FIG. 1 schematically illustrates an apparatus for refining magneticdomains of a grain-oriented electrical steel plate according to thepresent exemplary embodiment and FIG. 2 illustrates a steel platesubjected to magnetic domain refinement according to the presentexemplary embodiment. In the following description, a rolling directionor a steel plate moving direction means an x-axis direction in FIG. 2, awidth direction means a y-axis direction in FIG. 2 as a directionperpendicular to the rolling direction, and a width means a length of asteel plate for the y-axis direction. In FIG. 2, reference numeral 31indicates a radiation line formed continuously on the surface of a steelplate 1 with a groove shape dented by a laser beam.

Referring to FIG. 1, the apparatus for refining the magnetic domains ofthe grain-oriented electrical steel plate according to the presentexemplary embodiment stably performs permanent magnetic domainrefinement even if the refinement progresses at a high speed of 2 m/s ormore.

The apparatus for refining the magnetic domains of the present exemplaryembodiment includes a steel plate supporting roll position adjustingequipment for controlling a vertical direction position of the steelplate while supporting the steel plate 1 moving along a production line,a laser radiating equipment for melting the steel plate by radiating alaser beam to form a groove on the surface of the steel plate, and alaser room 20 for accommodating the steel plate supporting roll positionadjusting equipment and the laser radiating equipment separately fromthe outside and providing an operational environment for laserradiating.

In addition, the apparatus for refining the magnetic domains may furtherinclude a warp control equipment for allowing the steel plate 1 to movealong the center of the production line without horizontal biasing.

In addition, the apparatus for refining the magnetic domains may furtherinclude a tension control equipment for applying the tension to thesteel plate so as to allow the steel plate to be maintained in a flatstate without sagging.

In addition, the apparatus for refining the magnetic domains may furtherinclude a post-treatment equipment for removing hill-up and spatterformed on the surface of the steel plate in accordance with the laserbeam radiating.

The hill-up refers to a portion where molten iron is accumulated on bothsides of the groove portion at a predetermined height or more when thegroove is formed by radiating the laser beam to the surface of the steelplate. The spatter refers to molten iron generated during laser beamradiating and solidified on the surface of the steel plate.

The warp control equipment may include steering rolls 2A and 2B forshifting a moving direction of the steel plate 1, a warp measurementsensor 4 for measuring a degree (warp amount) when a width centerposition of the steel plate 1 deviates from the center of the productionline, and a steel plate center position control system 3 for controllinga moving direction of the steel plate 1 by rotating and moving shafts ofthe steering rolls 2A and 2B by calculating a detection signal of thewarp measurement sensor 4.

The warp measurement sensor 4 is disposed at the rear end of thesteering roll 2B to detect in real time the actual warp amount of thesteel plate passing through the steering roll.

It is possible to form the grooves on the surface of the steel plateover the entire width of the steel plate by straightly moving the steelplate along the center of the production line without horizontal biasingby the warp control equipment.

In the warp control equipment, the warp amount of the steel plate ismeasured by the warp measurement sensor 4 in the process before thegrooves are formed on the surface of the steel plate by laser radiating.The values measured by the warp measurement sensor 4 are output to thesteel plate center position control system, and the steel plate centerposition control system calculates the output values of the warpmeasurement sensor and rotates and moves the axes of the steering rolls2A, 2B according to the calculated warp degree. As described above, thesteering rolls 2A and 2B are rotated and moved, so that the movingdirection of the steel plate wound on the steering roll is adjusted.Thus, the warp amount of the steel plate is controlled, and the warpamount of the steel plate 1 may be controlled within ±1 mm.

The tension control equipment may include tension bridle rolls (TBRs) 5Aand 5B for guiding movement of the steel plate 1 while applying apredetermined tension to the steel plate 1, a steel plate tensionmeasuring sensor 7 for measuring the tension of the steel plate 1passing through the tension bridle roll, and a steel plate tensioncontrol system 6 for adjusting speeds of the tension bridle rolls 5A and5B according to the tension of the steel plate measured by the steelplate tension measuring sensor 7.

The steel plate tension measuring sensor 7 is disposed at the rear endof the tension bridle roll 5B and measures the actual tension of thesteel plate subjected to the tension via the tension bridle roll 5B inreal time.

In the present exemplary embodiment, the tension of the steel plate maybe set so as to prevent the breakage of the steel plate from occurringdue to excessively tension while making the shape of the surface of thesteel plate flat at the laser radiating position of the laser radiatingequipment.

In order to operate the tension control equipment by the steel platetension within a predetermined range, the tension control equipmentadjusts the speeds of the tension bridle rolls (TBR) 5A and 5B by thesteel plate tension control system 6 according to the tension of thesteel plate measured by the steel plate tension measurement sensor 7.Thus, the tension control equipment controls a tension error of thesteel plate 1 to be within the predetermined range to apply the tensionto the steel plate.

The steel plate passing through the tension control equipment flows intothe laser room 20, and is subjected to the magnetic domain refinementthrough the steel plate supporting roll position adjusting equipment andthe laser radiating equipment and then discharged to the outside of thelaser room 20. The laser room will be described below again.

In the present exemplary embodiment, a steel plate supporting roll 9 isdisposed directly below the laser radiating equipment in the laser room20, and deflector rolls 8A and 8B are provided on both sides with thesteel plate supporting roll interposed therebetween.

The moving direction of the steel plate 1 is shifted toward the steelplate supporting roll 9 by the deflector rolls 8A and 8B. While thesteel plate 1 passes through the deflector roll 8A, the moving directionis shifted toward the steel plate supporting roll 9 so that the steelplate 1 is in contact with the steel plate supporting roll 9, and thenthe moving direction is shifted toward the deflector roll 8B so that thesteel plate 1 moves through the deflector roll 8B.

The steel plate 1 is wound in an arc form along the steel platesupporting roll 9 by the deflector roll and passes while being insurface contact with the steel plate supporting roll. In order tominimize the variation of the focal distance of the laser beam due tothe vibration and waving of the steel plate during the radiating of thelaser beam, the steel plate needs to pass while being sufficiently insurface contact with the steel plate supporting roll, and in this state,the laser beam needs to be radiated to the steel plate progressing alongthe steel plate supporting roll. In the present exemplary embodiment, asthe steel plate is in surface contact with the steel plate supportingroll as described above, it is possible to accurately radiate the laserbeam to the steel plate.

The steel plate supporting roll position adjusting equipment may includea steel plate supporting roll 9 for supporting the steel plate 1 to thelaser radiating position of the laser radiating equipment, a brightnessmeasurement sensor 10 for measuring brightness of flame occurring whenthe laser is radiated to the steel plate in the laser radiatingequipment, and a steel plate supporting roll (SPR) position controlsystem 12 for controlling the position of the steel plate supportingroll 9 in accordance with the brightness of the flame measured by thebrightness measurement sensor 10.

The steel plate supporting roll position adjusting equipment isconfigured to support the steel plate 1 to the position of the laserradiating unit by the steel plate supporting roll 9 and entirelyvertically adjust the position of the steel plate 1 to be disposed in adepth of focus having high laser steel plate radiating efficiency sothat the brightness of the flame generated when the steel plate isradiated with the laser becomes the best. Further, the brightness of theflame generated when the steel plate is radiated with the laser ismeasured by using the brightness measurement sensor 10.

In the present exemplary embodiment, the steel plate supporting rollposition adjusting equipment may further include a distance measurementsensor 11 for measuring an actual distance from the optical system ofthe laser radiating equipment to the surface of the steel plate. Thesteel plate supporting roll position control system 12 calculates thebrightness of the flame detected from the brightness measurement sensor10 and the distance between the optical system and the surface of thesteel plate actually measured from the distance measuring sensor 11 tomore precisely control the position of the steel plate supporting roll9.

The warp control equipment, the tension control equipment, and the steelplate supporting roll position adjusting equipment serve to make steelplate conditions at the laser radiating position so that the lasergrooves may be formed precisely on the steel plate by the laserradiating equipment. In the steel plate at the laser radiating position,the center position of the steel plate needs to be positioned at thecenter position of the production line and the distance from the opticalsystem needs to be maintained at the set value.

The laser radiating equipment may include a laser oscillator controller13, a laser oscillator 14 for oscillating a continuous wave laser beam16, and an optical system 15.

As illustrated in FIG. 3, the optical system 15 may include a moduleplate 37 which is rotatably provided to give an angle of a laser beamradiation line in a width direction of the steel plate, a driver 36 forrotating the module plate 37, a header 39 which is provided in themodule plate 37 to radiate a laser beam applied from the laseroscillator 14 into the optical system 15, a polygon mirror 32 which isrotatably provided in the module plate 37 to reflect the laser beamradiated from the header 39, a rotary motor 33 rotatably driving thepolygon mirror 32, a light collection mirror 35 which is provided in themodule plate 37 to reflect the laser beam reflected from the polygonmirror 32 toward to the steel plate and collect the reflected laser beamin the steel plate, a driving motor 34 which is connected to the lightcollection mirror 35 to adjust a focal distance of the laser beam bymoving the light collection mirror 35, and a shutter 38 which isprovided in the module plate 37 to block selectively the module plate 37according to radiation of the laser beam.

The optical system 15 is configured by arranging the header 39, thepolygon mirror 32, the light collection mirror 35, and the shutter inthe module plate 37 forming an optical box to form one body. The laseroscillator 14 and the header 39 are connected to, for example, anoptical cable 41. As a result, the laser emitted from the laseroscillator 14 is transmitted to the header 39 via the optical cable 41.The header 39, the polygon mirror 32, the light collection mirror 35 arearranged at regular positions in the module plate 37 forming the opticalbox so as to reflect the laser beam 16 to a desired position. Asillustrated in FIG. 3, for example, the headers 39 are disposed at bothsides with the polygon mirror 32 therebetween to radiate the laser beamto the polygon mirror 32, respectively. Two light collection mirrors 35are disposed according to each laser beam reflected from the polygonmirror 32. The laser beam emitted from the header 39 is reflected fromthe polygon mirror 32 rotating according to the driving of the rotarymotor 33 to be transmitted to the light collection mirror 35. The laserbeam 16 reflected to the light collection mirror 35 is reflected fromthe light collection mirror 35 to the steel plate side through theshutter 38 to be collected on the surface of the steel plate 1. As aresult, the laser beam is periodically radiated on the surface of thesteel plate to form continuous grooves in a width direction.

The entire focal distance of the laser beam 16 by the optical system 15is adjusted by vertical movement of the steel sheet supporting roll 9,and misalignment of a horizontal focal distance is adjusted by thedriving motor 34 which is connected to the light collection mirror 35.

The shutter 38 is provided below the module plate 37 to close and openthe module plate 37. The shutter 38 is opened when the laser beam isradiated downward from the light collection mirror 35 to preventinterference with the laser beam and closed when the laser beam is notradiated to prevent external fumes or foreign substances from flowinginto the optical system 15.

If the warp amount of the steel plate is excessive, the steel platedeviates from the laser radiating position, and the steel platesupporting roll 9 is radiated with the laser to be damaged. As a result,in order to prevent the damage to the steel plate supporting roll, thelaser oscillator controller 13 turns on the laser oscillator undernormal operation conditions and controls the laser oscillator to turnoff when the steel plate warp amount is 15 mm or more.

The laser oscillator 14 may oscillate a Gaussian energy distributioncontinuous wave laser beam to transmit the oscillated laser beam to theoptical system 15. The optical system 15 radiates the transmitted laserbeam 16 to the surface of the steel plate.

The laser oscillator 14 and the optical system 15 may radiate the laserbeam to the surface of the steel plate to form grooves with an upperwidth, a lower width and a depth of 70 μm or less, 10 μm or less, and 3to 30 μm, respectively, and transmit laser energy density to the steelplate in the range of 1.0 to 5.0 J/mm² required for melting the steelplate so that a re-coagulation portion is generated to remain on theinner wall surface of the groove in the melting portion during laserradiating.

The optical system 15 has a function of controlling a laser scanningspeed to adjust an interval of the laser radiation line (31 in FIGS. 2)to 2 to 30 mm in the rolling direction. Therefore, the influence of aheat affected zone (HAZ) by the laser beam may be minimized, therebyimproving the iron loss of the steel plate.

The laser radiating equipment may be a structure for changing the angleof the radiation line of the laser beam radiated on the surface of thesteel plate with respect to the width direction of the steel plate. Inthe present exemplary embodiment, the laser radiating equipment maychange the angle of the radiation line of the laser beam to a range of±4° with respect to the width direction of the steel plate.

To this end, the laser radiating equipment may be a structure ofchanging the angle of the radiation line of the laser beam formed on thesurface of the steel plate with respect to the width direction of thesteel plate because the optical system 15 for radiating the laser beamto the steel plate is rotatable by a driving unit 36. As such, the angleof the radiation line of the laser beam is changed by the opticalsystem, and thus, the radiation line 31 by the laser beam is inclined inthe range of ±4° in a direction perpendicular to the rolling directionof the steel plate. Therefore, it is possible to minimize the decreasein the magnetic flux density due to the groove formation by the laser.

Further, in the present exemplary embodiment, the laser radiatingequipment controls the radiating position of the laser beam to the steelplate 1 to have a structure for preventing a back reflection phenomenonin which the laser beam radiated to the steel plate is reflected fromthe steel plate to enter the optical system or the laser oscillator.

To this end, as illustrated in FIG. 3, the laser radiating equipment maybe a structure in which the laser beam is radiated to a positionseparated at an angle (hereinafter, referred to as a separation angle Rfor convenience of description) along an outer peripheral surface at thecenter of the steel plate supporting roll 9 from a reference point P bysetting as a reference point P a laser beam radiating position when theradiating direction of the laser beam radiated from the optical system15 passes through the central axis of the steel plate supporting roll 9,with respect to the surface of the steel plate which progresses incontact with the surface of the steel plate supporting roll 9 in an arcform.

The reference point P is a point in which the steel plate meets a linepassing through the central axis of the steel plate supporting roll 9 inFIG. 3. When the radiating direction of the laser beam passes throughthe central axis of the steel plate supporting roll 9, the focal pointof the laser beam is adjusted to the reference point P. In this case, asthe radiating direction of the laser beam is orthogonal to a tangentialline of the steel plate supporting roll 9 at the reference point P, aback reflection phenomenon occurs, in which the laser beam reflectedonto the steel plate enters the optical system and the laser oscillatoras it is to damage the steel plate.

The laser radiating equipment according to the present exemplaryembodiment radiates the laser beam to the position separated by theseparation angle R at the reference point P and thus the laser beamreflected back from the steel plate is not incident to the opticalsystem. Therefore, it is possible to prevent the back reflectionphenomenon and to maintain the quality of the groove shape formed by thelaser beam.

In the present exemplary embodiment, the separation angle R may be setin a range of 3 to 7° along the outer peripheral surface at the centerof the steel plate supporting roll 9 with respect to the reference pointP.

When the separation angle R, which is the position at which the laserbeam is radiated, is smaller than 3°, a part of the laser beam reflectedback from the steel plate may be introduced into the optical system orthe laser oscillator. If the separation angle R exceeds 7°, the groovesare not properly formed by the laser beam and a formation defect of thegroove may occur.

As such, the laser radiating equipment according to the presentexemplary embodiment radiates the laser beam to the steel plate at aposition separated from the reference point P by a predetermined angle,thereby preventing the back reflection phenomenon and stably maintainingthe quality of the groove shape formed by the laser beam.

The laser radiating equipment may further include a molten iron removingequipment for removing fumes and spatters generated by radiating thelaser beam onto the steel plate.

The molten iron removing equipment may include an air knife 17 forspraying compressed dry air into the grooves of the steel plate toremove molten iron remaining in the grooves, and dust collecting hoods19A and 19B for sucking and removing the fumes and the molten iron. Thefumes generated during the laser radiating through the air knife and thedust collecting hoods are removed to prevent the fumes from flowing intothe optical system. The air knife 17 sprays compressed dry air having apredetermined pressure Pa into the groove of the steel plate 1 to removethe molten iron remaining in the groove. The compressed dry air in theair knife 17 preferably has a pressure Pa of 0.2 kg/cm² or more. Whenthe pressure of the compressed dry air is smaller than 0.2 kg/cm², it isimpossible to remove the molten iron in the groove and thus, the ironloss improvement effect can not be secured. The fumes and the spattersremoved by the air knife are removed by the dust collecting hoods 19Aand 19B disposed before and after the laser radiating position.

In addition, the laser radiating equipment may further include ashielding unit 18 for shielding reflected light, scattered light, andradiant heat of the laser beam from flowing into the optical system. Theshielding unit 18 shields the reflected light and scattered lightflowing into the optical system by reflection and scattering of thelaser beam 16 radiated onto the steel plate to prevent the opticalsystem from being thermally deformed by the radiant heat due to thereflected light and scattered light.

The laser room 20 is a room structure having an internal space andaccommodates the laser radiating equipment and the steel platesupporting roll position control equipment therein to isolate theequipments from the outside and provide an appropriate operatingenvironment for smooth driving thereof.

An inlet and an outlet of the laser room 20 are formed on the entranceand exit sides of the laser room 20 along the progressing direction ofthe steel plate. The laser room 20 has equipment for blocking the inflowof contaminants so that the internal space is not contaminated byexternal dust or the like. To this end, the laser room 20 has a positivepressure device 23 for raising the internal pressure beyond the outside.The positive pressure device 23 maintains the internal pressure of thelaser room 20 relatively higher than the external pressure. Thus, it ispossible to prevent foreign substances from flowing into the laser room20. In addition, air curtains 22A, 22B, 22C, and 22D are provided at theinlet and the outlet of the steel plate. The air curtain sprays air tothe inlet and the outlet, which are passages through which the steelplate enters and exits the laser room 20 to form a film, therebyblocking dust and the like from flowing into through the inlet and theoutlet. In order to prevent contamination in the laser room 20, a showerbooth 21 may be installed on the door, which is an entrance of the laserroom 20. The shower booth 21 removes foreign substances adhering to thebody of a passenger entering the laser room 20.

The laser room 20 is a space in which the process of refining themagnetic domains of the steel plate by the laser beam substantiallyprogresses, and it is necessary to minimize a change of the internalenvironment and maintain a proper environment. To this end, the laserroom 20 includes an optical system lower frame 24 for separating anupper space, in which the laser oscillator 14 and the optical system 15of the laser radiating equipment are located, from a lower space throughwhich the steel plate 1 passes, and a constant temperature and humiditycontroller 25 for controlling the internal temperature and humidity ofthe laser room 20.

The optical system lower frame 24 can more thoroughly manage anoperating environment of the main equipment such as the laser oscillator14 and the optical system 15. The optical system lower frame 24 isinstalled in the laser room 20 so as to separate the lower space of theoptical system through which the steel plate passes, from the upperspace of the optical system where the laser oscillator and the opticalsystem mirrors are located. The upper space of the optical system isalso separated from the inside of the laser room 20 by the opticalsystem lower frame 24 to prevent contamination and easily control thetemperature and humidity with respect to major equipments such as thelaser oscillator and the optical system.

The constant temperature and humidity controller 25 adjusts thetemperature and humidity inside the laser room 20 to provide a properenvironment. In the present exemplary embodiment, the constanttemperature and humidity controller 25 may maintain the internaltemperature of the laser room 20 at 20 to 25° C. and maintain thehumidity at 50% or less.

As described above, the internal space of the laser room 20 iscontinuously maintained at a temperature and humidity suitable for theoperating environment, and the process of refining the magnetic domainsmay be performed on the steel plate in an optimum state. Therefore, ahigh-quality product may be mass-produced under an optimal operatingenvironment required for the process.

The apparatus for refining the magnetic domains of the present exemplaryembodiment may further include a post-treatment equipment for removinghill-up and spatters formed on the surface of the steel plate.

Since the hill-up and spatters cause deterioration of an insulationproperty of the product and a space factor, the hill-up and spatters arecompletely removed through the post-treatment equipment to enhance thequality of the product.

The post-treatment equipment may include brush rolls 26A and 26Bdisposed at the rear end of the laser room 20 along a steel plate movingdirection to remove the hill up and spatters of the steel plate surface.The brush rolls 26A and 26B are rotated at a high speed by a drivingmotor, and a rotation speed and an interval with the steel plate arecontrolled by a current control system that controls a current value ofthe driving motor generated during operation to a set target value and abrush position control system that controls an interval between thebrush roll and the steel plate. The brush roll may be disposed on onlyone side of the steel plate having grooves formed by the laser beam, oron both sides of the steel plate. The brush rolls 26A and 26B arebrought into close contact with the surface of the steel plate and arerotated at a high speed to remove the hill up, the spatters, and thelike attached to the surface of the steel plate. As illustrated in FIG.1, a dust collecting hood 19C for discharging the hill up and thespatters removed by the brush roll is further provided near the brushrolls 26A and 26B. The dust collecting hood 19C sucks molten iron suchas the hill up and the spatters which are separated from the steel plateby the brush rolls 26A and 26B, and discharges the molten iron to theoutside.

Further, the post-treatment equipment may further include a cleaningunit 29 disposed at the rear end of the brush rolls 26A and 26B tofurther additionally remove the hill up and spatters remaining on thesurface of the steel plate by electrolytically reacting the steel platewith an alkali solution, and a filtering unit 30 connected to thecleaning unit to filter the foreign substances included in the alkalisolution of the cleaning unit from the alkali solution.

The hill up and the spatters of the steel plate are primarily removedvia the brush rolls 26A and 26B, and are secondarily removed via thecleaning unit 29. Thus, it is possible to enhance the product quality bymore completely removing the hill up and the spatters attached to thesurface of the steel plate.

The cleaning unit 29 is filled with an alkali solution therein, and thefiltering unit 30 is connected to one side. As the steel plate isprocessed through the cleaning unit, the hill up and the spattersremoved from the steel plate are accumulated in the internal alkalisolution, thereby deteriorating the cleaning performance of the steelplate. The filtering unit 30 circulates the alkali solution of thecleaning unit and removes the hill up and the spatters included in thealkali solution. The filtering unit 30 removes the hill up and thespatters to control the iron content of the alkali solution to 500 ppmor less. As such, it is possible to continuously process the steel plateby preventing deterioration of the cleaning performance of the cleaningunit.

Hereinafter, the process of refining the magnetic domains of theelectrical steel plate according to the present exemplary embodimentwill be described below.

The continuously conveyed steel plate is introduced into the laser roomthrough the warp control equipment and the tension control equipment toprogress at a velocity of 2 m/sec or more, and subjected to the magneticdomain refinement. The steel plate introduced into the laser room issubjected to the permanent magnetic domain refinement through the laserradiating equipment and then drawn out to the outside of the laser room.The steel plate drawn out to the outside of the laser room is sent tothe post-treatment after the hill up, the spatters, and the likeremaining on the surface are removed through the post-treatmentequipment.

In this process, the laser room in which the laser beam is radiated tothe surface of the steel plate is appropriately set and maintained inthe internal operating environment so as to provide an optimalenvironment for the magnetic domain refinement.

The laser room isolates the inside from the outside to block the inflowof external contaminants, and controls the internal temperature,pressure and humidity of the laser room according to the operatingenvironment for the magnetic domain refinement.

The internal pressure of the laser room is maintained to be higher thanthat of the outside so as to prevent foreign substances such as externaldust from flowing into the laser room. In addition, by forming a film ofair on the inlet and the outlet, which are the passages through whichthe steel plate is moved, it is possible to prevent foreign substancessuch as dust from flowing into the laser room in the process where thesteel plate progresses through the inlet and the outlet.

Further, the constant temperature and humidity controller installed inthe laser room maintains the temperature inside the laser room at 20 to25° C. and maintains the humidity at 50% or less, thereby providing anoptimum condition for the magnetic domain refinement by laser radiating.

As such, the laser room provides an optimal environment for laser beamradiating, and the steel plate is accurately positioned at the laserradiating position while passing through the warp control equipment, thetension control equipment, and the steel plate supporting roll positionadjusting equipment.

First, for the magnetic domain refinement, the steel plate is movedstraightly along the center of the production line without horizontalbiasing by controlling the progressing direction through the warpcontrol equipment.

The warp measurement sensor continuously detects the warp amount of thesteel plate, and when the steel plate is warped, the steel plate centerposition control system rotates and moves the shaft of the steering rollby calculating a signal detected by the warp measurement sensor to movethe steel plate to a correct position. Thus, by continuously controllingthe steering rolls according to the position of the steel plate, thesteel plate may be continuously moved without departing from the centerof the production line.

The steel plate is moved through the tension bridle roll for controllingthe tension via the steering roll. The tension of the steel platepassing through the tension bridle roll is detected by the tensionmeasurement sensor. The steel plate tension control system calculates ameasurement value detected by the tension measurement sensor andcontrols the speed of the tension bridle roll according to the settension. Thus, the tension of the steel plate to be moved may bemaintained continuously in accordance with the set range.

The steel plate passed through the tension bridle roll is introducedinto the laser room through the inlet of the laser room. The steel plateis shifted inside the laser room by the bridle roll and moved in a stateof being in close contact with the steel plate supporting roll locatedbetween the two bridle rolls.

The steel plate supporting roll moves the steel plate up and down toposition the steel plate in the depth of focus of the laser beam.

When the laser beam is radiated from the laser radiating equipment tothe steel plate, the brightness measurement sensor detects thebrightness of the flame on the steel plate surface in real time, and thesteel plate supporting roll position control system moves the steelplate supporting roll up and down according to the measured valuedetected by the brightness measuring sensor to allow the steel plate tobe positioned within the depth of focus of the laser beam. Thus, thelaser beam is effectively radiated onto the surface of the steel plate,to form a high-quality radiation line.

The laser oscillator controller turns on/off the laser oscillatoraccording to the warp degree of the steel plate. The laser oscillatorcontroller is connected to the warp measurement sensor, and determinesthat the steel plate deviates too much from the steel plate supportingroll when the warp amount of the steel plate measured from the warpmeasurement sensor is, for example, 15 mm or more to turn off the laseroscillator. Thus, it is possible to prevent the roll from being damagedby radiating the laser beam on to the surface of the steel platesupporting roll via the warped steel plate.

According to a command of the laser oscillator controller, the laserbeam generated by the laser oscillator is radiated onto the surface ofthe steel plate through the optical system. The laser oscillatoroscillates a TEM₀₀ continuous wave laser beam to transmit the oscillatedlaser beam to the optical system.

The optical system changes the direction of the laser beam and radiatesthe laser onto the surface of the steel plate to continuously form amolten groove on the surface of the steel plate, thereby performing themagnetic domain refinement.

While the surface of the steel plate is molten by the laser beamradiated to the steel plate through the optical system, the moltengroove is formed along the radiation line. In the present exemplaryembodiment, grooves having an upper width, a lower width and a depthwithin 70 μm, within 10 μm, and 3 to 30 μm, respectively, are formed onthe surface of the steel plate through the laser beam radiating.Simultaneously, the laser oscillator and the optical system transmit thelaser energy density within the range of 1.0 to 5.0 J/mm² required forthe melting of the steel plate to the steel plate so that are-coagulation part remaining on the inner wall surface of the groove ofthe melting part is generated during the laser radiating.

Further, by radiating the laser beam at a position R separated from thereference point P in the laser beam radiating process through theoptical system, the laser beam reflected back from the steel plate isnot incident to the optical system. Therefore, the back reflectionphenomenon may be prevented, and the incident light path of the laserbeam is not interfered by the reflected light, thereby maintaining thequality of the groove shape formed by the laser beam.

The optical system has a function of controlling a laser scanning speedto adjust the interval of the laser radiation lines with respect to therolling direction. Further, the optical system has a rotation functionto change the angle of the laser radiation line. In the presentexemplary embodiment, it is possible to adjust the interval of the laserradiation lines by 2 to 30 mm in the rolling direction by the opticalsystem, thereby minimizing the influence of the heat affected zone (HAZ)by the laser beam and improving the iron loss of the steel plate.Further, in the laser beam radiating process, the angle of the radiationline of the laser beam radiated on the surface of the steel plate may bechanged through the rotation of the optical system. In the presentexemplary embodiment, the optical system may change the angle of theradiation line of the laser beam into the range of ±4° with respect tothe width direction of the steel plate. That is, it is possible to formthe radiation line 31 of the laser beam so as to be tilted in the rangeof ±4° with respect to the y-axis direction in FIG. 2. Therefore, theradiation lines formed on the surface of the steel plate may be formedto be tilted in the range of 86 to 94° with respect to the rollingdirection. By forming the radiation line in such a manner as to betilted with respect to the y-axis direction, it is possible to minimizethe decrease in the magnetic flux density due to the groove formation bythe laser.

In the laser beam radiating process, while the steel plate is molten bythe laser beam, a large amount of fumes and molten iron spatters aregenerated. The fumes and the spatters contaminate the optical system,and if the molten iron remains in the groove, it is difficult to form aprecise groove and the iron loss is not improved, and as a result, theproduct quality is deteriorated. Thus, the compressed dry air is sprayedinto the grooves of the steel plate to remove the molten iron remainingin the grooves, and the fumes and the molten iron are directly suckedthrough the dust collecting hood to be removed. Therefore, it ispossible to prevent the fumes from flowing into the optical system inthe process of refining the steel plate magnetic domains, and to enhancethe magnetic domain refinement efficiency by rapidly removing the fumesand spatters. Further, it is possible to further prevent the scatteredlight and heat of the laser beam from flowing into the optical system ofthe laser radiating equipment during the laser beam radiating process.

The grooves are formed on the surface of the steel plate through thelaser beam radiating, and the steel plate subjected to the magneticdomain refinement is continuously moved and discharged to the outsidethrough the outlet of the laser room.

The steel plate discharged from the laser room is subjected t a processof removing the hill-up and the spatters attached to the surface of thesteel plate through the post-treatment process.

The steel plate is first in close contact with the steel plate whilepassing through the brush roll disposed outside the laser room toprimarily remove the hill up and the spatters by the brush roll rotatingat a high speed.

While the steel plate passing through the brush roll secondarily passesthrough the cleaning unit, the remaining hill up and spatters arefinally removed through the electrolysis reaction between the steelplate and the alkali solution. The steel plate in which the hill up andspatters are removed while passing through the cleaning unit is conveyedto the post-treatment.

TABLE 1 Iron loss improvement rate (%) After laser radiating After heattreatment 9.5 11.6 9.7 12.9 11.5 13.5 8.4 11.6 8.6 11.8 8.5 11.7

Table 1 above lists an iron loss improvement rate of the grain-orientedelectrical steel plate by grooves formed on the surface of the steelplate with a thickness of 0.27 mm by the continuous wave laser beamradiating according to Example. As listed in Table 1, in the case of thesteel plate subjected to the magnetic domain refinement by the Example,it can be seen that the iron loss is improved.

While the exemplary embodiments of the present invention have beenillustrated and described above, various modifications and otherexemplary embodiments may be made by those skilled in the art. All ofsuch modifications and other exemplary embodiments will be consideredand included in the appended claims so as not to depart from the truespirit and scope of the present invention.

DESCRIPTION OF SYMBOLS

1: Steel plate 2A, 2B: Steering roll (SR) 3: Steel plate center positioncontrol system 4: Warp measurement sensor 5A, 5B: Tension bridle roll 6:Steel plate tension control system 7: Steel plate tension measuring 8A,8B: Deflector roll sensor 9: Steel plate supporting roll 10: Brightnessmeasurement sensor 11: Distance measurement sensor 12: Steel platesupporting roll position control system 13: Laser oscillator controller14: Laser oscillator 15: Optical system 16: Laser beam 17: Air knife 18:Shielding unit 19A, 19B, 19C: Dust collecting hood 20: Laser room 21:Shower booth 22A, 22B, 22C, 22D: Air curtain 23: Positive pressuredevice 24: Optical system lower frame 25: Constant temperature andhumidity controller 26A, 26B: Brush roll 27: Motor current controlsystem 28: Brush position control system 29: Cleaning unit 30: Filteringunit 31: Radiation line 32: Polygon mirror 33: Rotary motor 34: Drivingmotor 35: Light collection mirror 36: Driver 37: Module plate 38:Shutter 39: Header

1. A method for refining magnetic domains of a grain-oriented electricalsteel plate, the method comprising: a steel plate supporting rollposition adjusting step of controlling a vertical direction position ofthe steel plate while supporting the steel plate; a laser radiating stepof melting the steel plate by radiating a laser beam to form grooves onthe surface of the steel plate; and a setting and maintaining step ofsetting and maintaining an internal operation environment of a laserroom in which the laser radiation is performed.
 2. The method forrefining magnetic domains of claim 1, wherein: the setting andmaintaining step includes steps of isolating the inside of the laserroom from the outside to block the inflow of external contaminants, andcontrolling an internal temperature, pressure, and humidity of the laserroom. 3-4. (canceled)
 5. The method for refining magnetic domains ofclaim 4, further comprising: a post-treatment step of removing hill upand spatters formed on the surface of the steel plate through the laserradiating step.
 6. The method for refining magnetic domains of claim 5,wherein: the post-treatment step includes a brushing step of removingthe hill up and the spatters smeared on the surface of the steel plateby a brush roll.
 7. The method for refining magnetic domains of claim 6,wherein: the post-treatment step further includes a cleaning step ofadditionally removing the hill up and the spatters remaining on thesurface of the steel plate by electrolytically reacting the steel platewith an alkali solution and a filtering step of filtering foreignsubstances included in the alkali solution removed from the steel platein the cleaning step from the alkali solution.
 8. The method forrefining magnetic domains of claim 4, wherein: in the laser radiatingstep, with respect to the surface of the steel plate progressing incontact with the surface of the steel plate supporting roll in the formof an arc, by setting as a reference point an radiating position of thelaser beam when the radiating direction of the laser beam passes througha central axis of the steel plate supporting roll, the laser beam isradiated to a position separated at a angle along an outer peripheralsurface from the center of the steel plate supporting roll at thereference point.
 9. The method for refining magnetic domains of claim 8,wherein: in the laser radiating step, the laser beam is radiated in arange of 3 to 7° separated from the center of the steel plate supportingroll along the outer peripheral surface thereof with respect to thereference point.
 10. The method for refining magnetic domains of claim4, wherein: the laser radiating step further includes an angle changingstep of changing a radiation line angle of the laser beam radiated onthe surface of the steel plate.
 11. The method for refining magneticdomains of claim 10, wherein: in the angle changing step, the radiationline angle of the laser beam with respect to the width direction of thesteel plate is changed to a range of ±4°.
 12. The method for refiningmagnetic domains of claim 4, wherein: the laser radiating step includesa blocking step of blocking fumes generated when the laser beam isradiated, a spraying step of spraying compressed dry air into thegrooves of the steel plate to remove molten iron remaining in thegrooves, and a dust collecting step of sucking and removing the fumesand the molten iron.
 13. The method for refining magnetic domains ofclaim 4, wherein: the laser radiating step includes a shielding step ofshielding scattering light and heat of the laser beam from flowing intothe optical system of the laser radiating equipment.
 14. An apparatusfor refining magnetic domains of a grain-oriented electrical steelplate, the apparatus comprising: a steel plate supporting roll positionadjusting equipment of controlling a vertical direction position of thesteel plate while supporting the steel plate; a laser radiatingequipment of melting the steel plate by radiating a laser beam to formgrooves on the surface of the steel plate; and a laser room ofaccommodating the steel plate supporting roll position adjustingequipment and the laser radiating equipment separately from the outsideand providing an operating environment for radiating the laser. 15-16.(canceled)
 17. The apparatus for refining magnetic domains of claim 14,wherein: the laser room accommodates the laser radiating equipment andthe steel plate supporting roll position adjusting equipment to form ainternal space to separate the equipments from the outside and has aninlet and an outlet formed at both sides in a progressing direction ofthe steel plate, and includes a positive pressure device for raising theinternal pressure of the laser room therein, an optical system lowerframe separating an upper space in which the optical system of the laserradiating equipment is positioned from a lower space through which thesteel plate passes, and a constant temperature and humidity controllerfor controlling the internal temperature and humidity of the laser room.18. The apparatus for refining magnetic domains of claim 17, furthercomprising: a post-treatment equipment for removing hill up and spattersformed on the surface of the steel plate.
 19. The apparatus for refiningmagnetic domains of claim 18, wherein: the post-treatment equipmentincludes a brush roll which is disposed at the rear end of the laserroom to remove the hill up and the spatters on the surface of the steelplate.
 20. The apparatus for refining magnetic domains of claim 19,wherein: the post-treatment equipment further includes a cleaning unitwhich is disposed at the rear end of the brush roll to additionallyremove the hill up and the spatters remaining on the surface of thesteel plate by electrolytically reacting the steel plate with an alkalisolution and a filtering unit which is connected to the cleaning unit tofilter foreign substances included in the alkali solution of thecleaning unit from the alkali solution.
 21. The apparatus for refiningmagnetic domains of claim 17, wherein: the laser radiating equipment hasa structure which is rotatable by the driver to change the angle of theradiation line of the laser beam with respect to the width direction ofthe steel plate by rotating the optical system with respect to the steelplate.
 22. The apparatus for refining magnetic domains of claim 17,wherein: the laser radiating equipment includes molten iron removingequipment for removing fumes and spatters generated by radiating thelaser beam to the steel plate.
 23. The apparatus for refining magneticdomains of claim 17, wherein: the laser radiating equipment includes ashielding unit of shielding laser reflecting light and scattering lightfrom flowing into the optical system.
 24. The apparatus for refiningmagnetic domains of claim 17, wherein: the laser radiating equipmentincludes an air knife for spraying compressed dry air into the groovesof the steel plate to remove molten iron remaining in the grooves, anddust collecting hoods for sucking and removing the fumes and the molteniron.